Med Java

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====== || Logical OR vs ?? Nullish Coalescing vs && Logical AND ======

The **||, ??, and &&** operators are used to perform different types of logical operations.

===== || (Logical OR) =====

The **||** operator returns the **first truthy value** it encounters or the **last value if none are truthy**:
<code javascript>
const a = 0;
const b = 'hello';
const result = a || b; // 'hello'
</code>

<note>
If you want to use || to return a boolean **true or false** value, you can simply convert the result to a boolean. One common way to do this is by using the Boolean constructor, or by using a [[java-script:double-not-operator|double NOT (!!) operator]]:
<code javascript>
const a = null; // falsy
const b = 'value'; // truthy

const result = Boolean(a || b); // returns true

// Or using the double NOT operator:

const resultWithNot = !!(a || b); // also returns true
</code>
These expressions will evaluate to true if either a or b is truthy, and false otherwise.
</note>

===== ?? (Nullish Coalescing) =====

The **??** operator returns the **right-hand operand when the left-hand operand is null or undefined**, and **the left-hand operand otherwise**. \\ 
It's useful for providing default values:
<code javascript>
const a = undefined;
const b = 'default';
const result = a ?? b; // 'default'
</code>

===== && (Logical AND) =====

The **&&** operator returns the **first falsy value** it encounters or the **last value if all are truthy**:
<code javascript>
const a = 'hello';
const b = 42;
const result = a && b; // 42
</code>

<note>
If you want to use && operator to return a boolean **true or false** value, you can simply convert the result to a boolean:
<code javascript>
const a = 'hello'; // truthy
const b = 42; // truthy

const result1 = Boolean(a && b); // true
const result2 = Boolean(a) && Boolean(b); // true
const result3 = !!a && !!b; //true
const result4 = !!(a && b); //true
</code>

Other example:
<code javascript>
const value1 = 'hello'; // truthy
const value2 = 0; // falsy

const result1 = Boolean(value1 && value2); // false
const result2 = Boolean(value1) && Boolean(value2); // true && false = false
</code>
</note>

===== Comparison =====

**||** is generally used for providing a fallback value when dealing with falsy values (**false, 0, empty strings, null, undefined, NaN**). \\ 

**??** is more specific than || because it only falls back for **null** or **undefined**, not for other falsy values like 0 or an empty string ''. \\ 

**&&** is used to ensure that multiple conditions are truthy. \\ 

Example:
<code javascript>
const value = 0;
const fallback1 = 'fallback';

const result1 = value || fallback1; // 'fallback' because 0 is falsy
const result2 = value ?? fallback1; // 0 because 0 is not null or undefined
const result3 = value && fallback1; // 0 because 0 is the first value, and it's falsy
</code>

<note tip>
See also [[java-script:bitwise-or-bitwise-and-ternary-optional-chaining-operators|bitwise operators]].
</note>